The present invention relates to a method for determining the bending angle of a sheet which has been bent along a bending line, for example on an angle-bending or folding machine, comprising the steps of generating at least one light beam, using these light beams to project two points or line segments onto a part of the sheet to be checked which lies on one side of the bending line, the beams formed an angle of incidence which is known in advance with the bending line of the sheet, imaging these points or line segments onto receiving means, and determining the distance between the points or line segments which have been projected onto the receiving means.
A measuring method of this type is known, inter alia, from Dutch Publication 8301528. According to the method described in this document, a relative angle is determined, that is to say the difference between the bending angle in a first, generally as yet unbent position of the sheet which is to be deformed and in a second position of the sheet which is to be deformed. Therefore, two measurements are required in order to measure this angles a first reference measurement and a second measurement which gives the change in angle. The angle to be determined in this way is therefore only equivalent to the bending angle if the sheet is flat in the first position. Consequently, it is not possible for example, to determine the bending angle of a workpiece which has already undergone preliminary bending through an angle which is not known. Therefore, the workpiece cannot be bent in a controlled way until a desired bending angle is reached.
Another drawback of this method is that to calculate the bending angle, inter alia the geometric relationships of the bending process are required; consider the geometry of the tool and the point of incidence of the light in the starting situation. Since the measurement is dependent on parameters which are not always known and/or which may vary during the bending, there are errors in the measured angle and these errors can only be corrected with the aid of factors which are dependent on, for example, the thickness of the bent sheet, the material from which the sheet is made and the angle which is to be measured itself. This will be explained in more detail with reference to the figures.
The object of the present invention is to provide a method and device for determining a bending angle which is not dependent on the geometry of the tool. Furthermore, the measurement should not be dependent on a starting position in which preliminary measurements have to be carried out. Consequently, the bending angle can be determined without the workpiece having to be supplied in a configuration which is known in advance. Moreover, it is not necessary for the workpiece to be deformed before the angle can be determined.
According to the present invention, the object is achieved by the fact that the beams lie in two different, parallel detection planes, the distance between which is known, and in that a measurement of the bending angle is determined from the distance between the points which have been projected onto the receiving means, the known angles of incidence of the beams and the known distance between the detection planes. The use of the parallel detection planes according to the invention allows an absolute measurement to be carried out, in which the only parameters required are the distance between the detection planes, the angles of incidence of the beams and the distance between the projected points. This contrasts with the relative measurement according to the prior art.
It is observed that DE 4 312 565 A1 discloses a folding machine for folding a plane workpiece along a folding line, in which by means of a light source a line is projected on each part lying at each side of the folding line of the workpiece. In contrast to the invention the folding angle is derived by interpreting said two lines at both sides of the folding line by means of image processing and a two-dimensional camera.
According to the invention, however, two points or line sections are projected on one part at one side of the folding line and the folding angle is derived from the difference in height from said two points or line sections and the fixed distance between the parallel detection planes.
In a preferred embodiment, the bending line is parallel to the detection planes, and the angles between the two beams and the bending line are equal. This has the advantage that the mathematics required in order to determine a measurement of the bending angle from the said data remains simple.
To enable only one receiving means to be used, it is desirable for the images of the points or line segments which have been projected onto the sheet, during use, always to be sufficiently far apart on the receiving means that the position of both can be determined. In a preferred embodiment, this is achieved by the fact that the points or line segments which are projected onto the sheet are offset with respect to one another in a direction parallel to the bending line.
To simplify the projection of the line segments, it is preferably for the line segments to form part of one line. To obtain the aforementioned offset of the segments, it is therefore necessary in this case for the line to include a xe2x80x9cstepxe2x80x9d.
The bending of the sheet which is to be bent does not always have to be identical on both sides of the bending line with respect to a bending plane. Therefore, it is preferable for the measurement according to one of the abovementioned methods to be carried out on both sides of the bending line, for partial bending angles on both sides of the blade to be determined as an intermediate result, and for the bending angle to be determined on the basis of these partial bending angles.
The invention also relates to a method for bending a sheet at a defined angle, comprising the steps of a) lowering an angle-bending blade to a defined height, a supporting sheet being placed on both sides of the displacement plane of the angle-bending blade and this angle-bending being carried out as a function of an angle measurement according to one of the preceding methods, b) completely or partially removing the pressure which the angle-bending blade exerts on the sheet, c) using one of the preceding methods to determine the bending angle of the sheet which has been reached, d) returning to step a) if the desired bending angle has not yet been reached, and e) stopping the bending when the desired bending angle has been reached.
The invention also relates to a method for determining the material deformation in a processing machine, in particular the angle between a surface of the said material and a reference plane, in which one of the abovementioned methods is used.
Moreover, the invention relates to a device for determining a bending angle of a sheet which has been bent along a bending line, comprising at least one light source for generating at least one light beam, in such a way that these beams project two points or line segments onto the sheet to be checked, the beams forming a predetermined angle with the bending line of the sheet, and receiving means for detecting the points or line segments which have been projected onto the sheet, by means of which the distance between these points or line segments can be determined.
According to the present invention, this device is characterized in that there are detection planes in which the beams lie and which are at a known distance from one another, in that there is an optical device which guides the light from the detection planes to the associated receiving means, and in that the processing device comprises a computing unit which calculates the bending angle from the distance between the projected points, the known angles of incidence of the beams and the known distance between the detection planes.
In a preferred embodiments, the bending line is parallel to the detection planes enclosed by the beams, and the angles between the two beams and the bending line are equal.
To enable the measurement to be carried out using one receiving means, it is preferable for the images on the receiving means of the points or line segments which have been projected onto the sheet, during use, always to lie sufficiently far apart for it to be possible to determine the position of both using the said receiving means. This may, for example, be achieved by ensuring that the points or line segments which are projected onto the sheet are offset with respect to one another in a direction parallel to the bending line. When using line segments, it may be advantageous for these segments to form part of one continuous line. To ensure that the abovementioned offset is still obtained, the line can include a xe2x80x9cstepxe2x80x9d.
As stated above, for accurate determination of the bending angle it is advantageous to determine partial angles on two sides of the bending line. For this purpose, in one embodiment the device is characterized in that the means required are designed in such a way that measurement can be carried out on both sides of the bending line, that partial bending angles on both sides of the bending line are determined as an intermediate result, and that the computing unit determines the bending angle on the basis of these partial bending angles.
The invention furthermore relates to a device for determining the material deformation in a processing machine, in particular the angle between a surface of the said material and a reference plane. This device is characterized in that one or a combination of the properties of the devices from Claims 10 to 16 is used for this purpose.
Furthermore, the invention relates to an angle-bending blade which can be used in a folding machine. This angle-bending blade comprises a device according to one of the abovementioned devices.
The invention will be discussed in more detail below with reference to the drawings, in which:
FIG. 1 diagrammatically depicts a cross section through a folding machine and an angle-ending blade according to one embodiment of the present invention; and
FIG. 2 diagrammatically depicts the way in which the bending angle can be calculated from the known and measured parameters according to one embodiment of the invention.